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BVC Glass Problems

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Posted by Ron White on April 1, 2003 17:22:06 UTC

I ground a 16" mirror from BVC glass. I Bought a 16" plano and ground it to F4. this blank is made from 1/4" thick sheets fused together when I cut thru the first layer and into the second it had massive voids-- very ugly --( I don't mean bubbles these areas were like 1 to 2 square inches in area) the zone area between the sheets of fused glass polished different from the rest of the of the mirror surface so figuring was a bear. I got the mirror to an 1/8 wave except for the fused area but the voids made it to ugly to have coated. I did mount and star test the mirror and the views were awesome with the 6" center / fused / ugly / area blocked off. I had a problem with scratches because of chips of glass from the void edges flaking off. I solved this By stopping the grinding at 12micron grit and polishing from there.

This blank was the second using this glass the first was a 12" BVC generated F5 I didn't have any problem with voids with this blank but I had a lot of problems with scratches at fine grinding from the ceramic tile tool I was using.
after polishing the mirror had bad astignatism. I was re grinding it when the blank stuck, went sailing off of the tool and exploded.
I don't know if the problems I had with the 12" was my fault or the glass but I will never use this material again.
I would like to hear feed back from any one using these blanks because there isn't much info out there. Thanks

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